Heat exchangers are used in the vast majority of motor vehicles that are powered by an internal combustion engine. Heat exchangers may be used for engine cooling and for internal climate control. Most heat exchangers include a header and a tank at each end of the header. It has become common practice to manufacture the tank from a plastic material and the header from a heat conductive metal material such as aluminum. The plastic tank is mechanically joined to the header. It is vital that the junction between the tank and header be leak-free and durable in spite of the corrosive fluid that flows through the heat exchanger.
With reference to FIG. 1, a junction 11 of heat exchanger 10 known in the prior art is now illustrated. It is now common practice to provide a channel 12 in the header 14 and a foot 16 at the lower end of the tank 18 of heat exchanger 10. The tank foot 16 is sized to be received in the channel with a sealing gasket 20 interposed between the tank and header. The channel 12 has an outer flange 22 with a plurality of tabs 24 that are clinched about the foot to retain the foot within the channel.
Several disadvantages exist with the present tank and header junction 11 constructions. Firstly, the tab 24 is bent from the outer flange 22 to bend about a corner 26 of the foot 16. The clinching operation of the tabs uses the corner 26 of foot 16 as a fulcrum resulting in stress exerted on the plastic tank foot 16. Excess stress can result in cracks in the foot ruining the integrity of the tank.
Furthermore, the clinch process is sensitive to the tab height variations due to manufacturing tolerances. The applied clinching force is applied as close to the top 25 of the header tabs 24 as possible to provide maximum mechanical advantage. The applied clinching force may then, depending on the height of the tabs, exert different levels of stress on the foot corner 26 that is used as a fulcrum. The tab height must be limited to decrease the stress exerted on the fulcrum point 26. Due to manufacturing tolerances, one tab may be shorter than others. Because of the short height of the tabs, the applied force to effectively bend the shorter tab must be significantly higher than for the other tabs due to the short tab heights. Consequently, the force used to bend all the tabs is the force needed to bend the shortest tab is undesirable in that it may stress the foot of the tank.
In addition, the tank foot is provided with a chamfer 28 along its side wall 30 for ease of installation of the tank into the header channel. The chamfer provides a pocket 32 into which the sealing gasket 20 may be squeezed and displaced around a bottom corner 34 of the foot during the clinching operation. The resulting high compression of the sealing gasket may damage the gasket or render an inadequate seal.
The above problems are cumulative. Consequently, most leakage and warranty problems in heat exchangers of the above described construction occur in the junction between the tank and header.
What is needed is a junction construction for a heat exchanger that is easily assembled with a minimum amount of stress exerted on the tank foot during assembly and that eliminates the above described problems.
What is also needed is a method for assembling a heat exchanger that provides for a reliable and securely sealed junction.